These studies involve: 1) the effects of various concentrations of AVP or OT on contractile parameters in rat proximal epididymides in vitro and the importance of Mg++ concentration to this process; 2) the nature of receptors mediating any effect caused by AVP and OT. That is, by using various concentrations of peptide antagonists specific for OT receptors, AVP receptor subtype V18 and AVP receptor subtype V2 the investigators will note which receptors are responsible for the contractile response observed and to what extent cross-reactivity occurs between these two hormones and their receptors; 3) the involvement of prostaglandins in mediating the contractile response to AVP and OT in the presence of various concentrations of nonsteroidal anti-inflammatory agents; and 4) autoradiographic localization of epididymal binding sites for 3H-AVP and 3H-OT in the rat. The data obtained in these studies will demonstrate the role of AVP, OT and prostaglandins in epididymal contractility and thus sperm transport through this organ.